Battery won't charge while connected to mains

Hello

i have an iPhone 3G that i use for music

ist a 16GB model and i love it

strangely last night i connected it to the mains to charge it over the night

when i got awake the phone was at 5% ....

so i thought the cables weren't properly connected..

grabbed my iPod charger and the same thing , it charged up to 12% and then suddenly goes back to 3% .... after 15 mins it stayed on 6% ....

so i tried another charger and another cable ...

iv'e cleaned out the dock connector and take a look at the battery . it isn't swollen up so i don't think the battery is the problem

what i did a few days ago is i removed the processor speed limit an ran it up to its potential speed 600MHz ... after a day i realized poor battery time so i revert it to the original speed and did an full recovery to make sure everything was ok

after that i had a day of use out of it and did not notice anything strange ..

so did i broke my main board perhaps ?

i'm on vacation now so cant do much but i have at home a new dock connector and a working 16GB motherboard to put in but , i'm curious did i do something wrong .. until that time i'm running no jailbreaks on the phone